Modular device for multiple reception of a modulated signal

ABSTRACT

A reception device includes a number of reception paths and a decoder. The reception paths are sequenced and each reception path includes a calculation module embodied to deliver a combined confidence index and a combined data stream, from the confidence index and the equalized data stream for the current path, as well as, for the subsequent reception paths after the first path, from the combined confidence index and the combined data stream, for the preceding path. The decoder is embodied to only process the combined confidence index and the combined data stream, provided by the calculation module in the last path.

RELATED APPLICATIONS

The subject application is a U.S. National Stage application that claimsthe priority of International Application No. PCT/FR03/00405, filed on 7Feb. 2003, which claims the priority of French National Application No.:02 01779, filed on 13 Feb. 2002.

FIELD OF THE INVENTION

The present invention relates to a modular device for multiple receptionof a modulated signal.

BACKGROUND

Devices of this type are used, for example, for receiving signalsmodulated by orthogonal frequency division multiplexing, commonly knownas OFDM or COFDM signals.

Conventionally, digital signals, such as television programmes, arecoded, in order to be broadcasted by radio relay channel.

Communication by radio relay channel generates propagationirregularities as a result of reflections and echoes caused by theenvironment, among other things.

It is thus possible to receive a plurality of data streams,corresponding to the reception of a single source signal, in a pluralityof different ways, this phenomenon being commonly known as multiplereception.

Multiple reception may be a space diversity, by separating tworeceivers, so that the fading of the source signal is relativelydecorrelated at these two points, but it may also be a polarisationdiversity, a frequency diversity or a temporal diversity, or else acombination of these techniques.

When the various multiply received streams, all representative of asingle source signal, are combined, a better-quality data stream may beobtained than if a single stream had been used.

The received streams may be combined by a plurality of methods. Forexample, the best stream may be retained, or else a threshold may bedefined from which a stream may be used.

An effective method of combining multiply received streams consists inproducing weighted additions.

A confidence index is thus attributed to each stream, which is processedas a function of said index, all of the processed streams then beingadded, in order to issue a total data stream.

The best combination or “maximum ratio combining”, commonly known asMRC, allows the maximum signal-to-noise ratio to be obtained at theoutput.

This combination is defined, in particular, in the article “LinearDiversity Combining Techniques” by D. G. Brennan, published in June 1959by the ME (pp. 1075 to 1102).

The teaching of this article defines a combined datum or optimal ratiodatum equal to the weighted data source for each channel.

The results obtained at the end of these combinations are sent to aweighted input decoder, such as a Viterbi decoder, for example, whichdecodes the total data stream in the conventional manner.

A device implementing a method of this type is also disclosed in thepatent FR-B-2 788 048.

In this device, each reception channel issues a confidence index fromthis channel and data which is more or less amplified, as a function ofthis index.

All of the data and the confidence indices are used in a singlecombination step, issuing a total confidence index and a total datastream that are adapted to a weighted input decoder.

It thus appears in this device that the architecture is based on thejuxtaposition of processing channels and on the use of a final, multipleinput combination stage.

As a result, numerous functions are duplicated on each channel, and thesummation/weighting function has to be incorporated on each channel orbe implemented by a single, specially dimensioned circuit, whichrequires a considerable surface area for the substrate duringproduction, in the form of electronic components.

It appears, therefore, that the existing devices are large, complex andexpensive.

SUMMARY OF THE INVENTION

The object of the present invention is to respond to theses problems byproviding a modulable receiver and optimising the electronic substrate.

The present invention relates to a device for receiving a Hertz signal,said device comprising a plurality of reception channels and a decoderwith weighted inputs, each reception channel receiving at the input adata stream corresponding to said transmitted Hertz signal, andcomprising a module for determining a confidence index and anequalisation module which is able to issue a stream of equalised datafrom the received data stream and from said confidence index,characterised in that the reception channels are sequenced, and in thateach reception channel comprises a calculation module which is able toissue a combined confidence index and a stream of combined data fromsaid confidence index and from said stream of equalised data for thecurrent channel and also for the reception channels following the firstchannel, from the combined confidence index and the stream of combineddata for the preceding reception channel, the outputs of the calculationmodule of the last channel forming a total confidence index and a totalstream of combined data, said decoder with weighted inputs being able toprocess the combined confidence indesand the stream of combined data,issued only from the calculation module of the last channels.

According to other characteristics of the invention:

-   -   each calculation module comprises elementary calculation means,        allowing a combined confidence index CCSI_(i), such that        CCSI_(i)=CCSI_(i−1)+CSI_(i), to be issued from the confidence        index CSIi for the current channel and the combined confidence        index CCSI_(i−1) for the preceding channel;    -   the calculation module for each channel comprises elementary        calculation means, allowing a weighting coefficient al such that        α₁=CCS_(i−1)/CCSI_(i), as well as its complement relative to 1,        to be defined from the combined confidence indices CCSI_(i) and        CCSI_(i−1) for the current and preceding channels;    -   the calculation module for each channel comprises elementary        calculation means, allowing a stream of combined data CZ_(i),        such that CZ_(i)=α_(i)×CZ_(i-1)+(1−α_(i))×Z_(i), to be issued        from the stream of combined data CZ_(i-1) for the preceding        channel, the data stream Z_(i) and the weighting coefficient        α_(i) for the current channel;    -   the calculation module for each channel comprises at the input a        synchronisation module which is able to synchronise the stream        of combined data and the combined confidence index issued by the        preceding reception channel, and the data stream and the        confidence index issued by the current reception channel;    -   each reception channel also comprises means for formatting the        received data stream, comprising at least one of the following        elements: a tuner, an amplifier and a converter;    -   the device is produced, at least in part, using programmed        components and/or dedicated components comprising connections        which are able to implement the functions of this device;    -   the device comprises at least one microprocessor or        microcontroller.    -   the device is able to receive at the input a multi-carrier        signal.    -   said input signal is an OFDM or COFDM signal; and    -   the device is able to receive television signals.

A better understanding of the invention will be facilitated by thefollowing description, given solely by way of example, with reference tothe accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a receiver according to the invention,and

FIG. 2 is a schematic diagram of a calculation module used in a deviceaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS

FIG. 1 shows schematically the architecture of a device for multiplyreceiving a television signal.

As shown, the device I comprises a plurality of sequenced receptionchannels, 1 to N.

Conventionally, each reception channel i is associated with an antenna 5_(i), allowing a data stream to be received, all of the received streamscorresponding to a single television signal.

For example, it is possible to distribute the ants 5 i spatially suchthat the fading of the source signal is different on each antenna, andsuch that the received data streams are decorrelated from one another.

Similarly, the antennas 5 _(i) may be able to receive differentpolaisations, such that each of the streams received for each of thereception channels, 1 to N, corresponds to the same initial signal, butwith a different polarity.

Conventionally, each reception channel i comprises at the input meansfor formatting the received data stream, such as a tuner 10 _(i), anamplifier and optionally a converter 12 _(i.)

Tuners 10 _(i) allow the received signal to be transposed into anintermediate frequency that is more favourable for the processing to becarried out, and amplifiers and Converters 12 _(i) allow the receivedstream to be amplified and converted into a stream of digital data.

For each channel i, the formatting means issue at the output a digitalsignal Y_(i), corresponding to the data stream received on the antenna 5_(i), amplified and digitised.

Each reception channel then comprises a demodulator 14 _(i), comprisinga calculation module 20 _(i) which allows a confidence index CSI_(i),which relates to said module, to be issued from the signal Y_(i),corresponding to the received data stream.

The confidence index CSI_(i) is conventionally calculated by determiningthe signal-to-noise ratio of the received data stream. Each of thedemodulators 14 _(i) also comprises an equalisation module 22 _(i),which allows a stream of equalised data Z_(i) to be issued from thesignal Y_(i), corresponding to the arriving data stream, and from thecorresponding confidence index CSI_(i).

According to the invention, each reception channel also comprises acalculation module 24 i, allowing a combined confidence index CCSI_(i)and a stream of combined data CZ_(i) to be issued.

Each calculation module 24 _(i) receives at the input the confidenceindex CSI_(i) for its channel and the stream of equalised data Z_(i) forits channel.

Moreover, each calculation module 24 _(i), except for the module 24 _(i)for the first reception channel, also receives the stream of combineddata CZ_(i-1) and the combined confidence index CCSI_(i-1), issued bythe calculation module 24 _(i-1) for the preceding channel.

Thus, the module 24 ₂ receives the results issued by the module 24 ₁,and the module 24 _(N) receives the results issued by the module 24_(N-1).

The calculation module 24 ₁ for the first reception channel receives atthe input only the data stream Z₁ and the confidence index CSI₁ for itsreception channel. The inputs provided for the results issued by apreceding channel are predetermined and set to zero.

In an iterative construction, the calculation modules 24 _(i) aretherefore constructed in a cascade from one channel to the other, so asto use the results obtained in one channel for the calculations for thefollowing channel.

Using the signals that they receive at the input, the calculationmodules 24 _(i) each issue the combined confidence index CCSI_(i) andthe stream of combined data CZ_(i).

The information issued by the calculation module 24 _(N) for the lastreception channel forms a total confidence index and a total stream ofcombined data corresponding to an optimal ratio combined datum or“maximal ratio combining” (MRC). These two signals alone are sentdirectly to a decoder, with two weighted inputs, 30 of the device. Thisdecoder 30 may be a Viterbi decoder or an iterative decoder, known as aturbo code decoder, and allows an optimised signal to be issued as afunction of the data streams received by each of the reception channels.

A device of this type is particularly suitable for receiving signalscomprising a plurality of frequencies, each carrying a portion of theinformation and being commonly known as multi-carrier signals.

The various channels each then receive all of the carriers, and therisk, associated with selective attenuation, of information loss isreduced

In particular, in the multiple reception of a multi-carrier signal, suchas an OFDM or COFDM signal, each reception channel receives a modulatedsignal comprising a plurality of carriers grouped together in symbols.

In order to reconstruct the emitted signal, the signals are combinedaccording to carrier, a plurality of signals corresponding to thereception on the various channels or the same carrier in the same symbolare thus combined, such that the last channel issues a total stream ofcombined data comprising the same number of symbols and, within saidsymbols, the same number of carriers as the emitted signal.

The elementary functions of an embodiment of a calculation module 24_(i) are described in greater detail with reference to FIG. 2.

As previously stated, the calculation module 24 _(i) receives at theinput the combined confidence index CCSI_(i-1) and the stream ofcombined data CZ_(i-1), both issued by the preceding reception channeli-1. This module also receives the stream of equalised data Z_(i) andthe confidence index CSI_(i) that correspond to the current channel i.

First of all, all of theses inputs are introduced into a synchronisationmodule 32 _(i), which allows them to be synchronised to a single tiereference. Generally, the data issued from the preceding channel isadjusted, so as to synchronise it with the data for the current channel.The preceding combined confidence index CCSI_(i-1) and the currentconfidence index CSI_(i) are then introduced into a summer 34 _(i),which issues the current combined confidence index CCSI_(i), such thatCCSI_(i)=CSI_(i)+CCSI_(i-1).

The combined confidence index CCSI_(i-1) for the preceding channel andthe current combined confidence index CCSI_(i) are then introduced intoa divider 36 _(i).

The divider 36 _(i) then issues at the output a weighting coefficientα_(i), defined by α_(i)=CCSI_(i-1)/CCSI_(i).

The coefficient α_(i) is then introduced into a subtracter 36 _(i), inorder to issue the complement of α_(i) relative to 1, by carrying outthe process 1−α_(i).

The stream of combined data CZ_(i-1) and the weighting coefficient aiare then introduced into a multiplier 40 _(i).

The datum Z_(i) and the complement of α_(i) relative to 1 are alsointroduced into a multiplier 42 _(i).

Finally, the results of the multipliers 40 _(i) and 42 _(i) areintroduced into a summer 44 _(i), which issues a current combined datumCZ_(i), such that:CZ_(i)=α_(i)×CZ_(i-1)+(1−α_(i))×Z_(i)

The module 24 _(i) thus issues a combined confidence index CCSI_(i)equal to the sum of confidence indices for each of the channels 1 to iand a stream of combined data, such that:

${CCSI}_{i} = {\sum\limits_{j = 1}^{i}{CSI}_{j}}$andCZ_(i)=α_(i)×CZ_(i-1)+(1−α_(i))×Z_(i), wherein α_(i)=CCSI_(i-1)/CCSI_(i)

The equations thus obtained are generic equations which may be appliedto all of the reception channels.

Thus, for the first reception channel, the application of these formulaeallows the following to be determined:CCSI₁=0+CSI₁=CSI₁ andα₁=0 such that CZ₁=α₁×0=(1−α₁)×Z₁=Z₁

Similarly, the calculation module 24 _(N) for the last transmissionchannel N issues a combined confidence index CCSI_(N) equal to the sumof the confidence indices for each of the channels 1 to N and a streamof combined data from data and confidence indices for each channel, suchthat:

${CCSI}_{N} = {\sum\limits_{j = 1}^{N}{CSI}_{j}}$andCZ_(N)=α_(N)×CZ_(N-1)+(1−α_(N))×Z_(N), wherein α_(N)=CCSI_(N-1)/CCSI_(N)

This data forms the total combined confidence index and the total streamof combined data that are introduced into the Viterbi decoder 30, whichissues at the output an optimised signal relative to the received datastreams.

It appears, therefore that the total combined datum for the last channelmay be expressed as follows:

${{CZ}_{N} = {\sum\limits_{j = 1}^{N}{\frac{{CSI}_{i}}{{CCSI}_{N}}Z_{j}}}},$and corresponds to an optimal ratio combined datum, as defined by theteaching of the aforementioned article by Brennen.

The output signal may then be used in the conventional manner, forexample, this data is demultiplexed and decoded in order to issuevarious types of data, such as audio data and video data.

Advantageously, the demodulators 14 ₁ to 14 _(N) may be configured usinga limited number of demodulators, associated with buffer memories andused in a recursive manner with all of the reception channels.

The demodulators 14 _(i) may be configured using conventional electroniccomponents, FPGA-type programmed components, ASIC-type componentsdedicated to these functions, or microprocessor components, such asDSPs. Similarly, all of the reception channels may, in their entirety orin part, be produced using programmed components, the connectionswhereof are configured for implementing these functions.

Moreover, the means for formatting the received data streams maycomprise elements other than those described, and may be arrangeddifferently, depending on the situation.

Furthermore, the elementary functions forming the described calculationmodules may be constructed or produced differently from the describedembodiment.

It appears, therefore, that owing to the iterative construction of thereception channels, a device according to the invention allows thenumber of components used to be reduced and utilises a modulablearchitecture that may easily be adapted to the number of receptionchannels.

Moreover, apart from the first and last ones, the various receptionchannels may be combined in different orders.

Although the invention has been described in the context of thereception of television signals, it also applies to the multiplereception of any signal for transmitting digital information, such asmobile telephony signals or any other digital signals.

Similarly, the transmitted signal may be modulated in various formats,such as OFDM, COFDM, QAM and QPSK.

1. An apparatus for receiving a modulated signal, said apparatus comprising: a plurality of successive reception channels configured to receive a data stream corresponding to the modulated signal, each reception channel comprising: a module for determining a confidence index of the received data stream, and an equalization module configured to issue a stream of equalized data from the received data stream and from the confidence index, a calculation module, wherein the calculation module of the first reception channel is configured to issue a combined confidence index and a stream of combined data from the confidence index and from the stream of equalized data of the first reception channel, and wherein the calculation module of each reception channel following the first reception channel is configured to issue a combined confidence index and a stream of combined data from: the confidence index of the current channel, the stream of equalized data of the current channel, the combined confidence index of the preceding channel, and a stream of combined data of the preceding reception channel, a decoder configured to process the combined confidence index and the stream of combined data issued only from the calculation module of the last channel.
 2. The apparatus according to claim 1, wherein the calculation module of each reception channel following the first reception channel comprises a first elementary calculation means configured to generate the combined confidence index (CCSI_(i)) from: the confidence index (CSI_(i)) of the current channel, and the combined confidence index (CCSI_(i-1)) of the preceding channel; and wherein CCSI_(i)=CSI_(i)+CCSI_(i-1).
 3. The apparatus according to claim 2, wherein the calculation module of each reception channel following the first reception channel comprises a second elementary calculation means configured to generate a weighting coefficient α_(i) and the complement of the weighting coefficient α_(i) relative to 1 from the combined confidence indices CCSI_(i-1) and CCSI_(i-1), for the current and preceding reception channels and wherein α_(i)=CCSI_(i-1)/CCSI_(i).
 4. The apparatus according to claim 3, wherein the calculation module of each reception channel following the first reception channel comprises a third elementary calculation means configured to generate the stream of combined data CZ_(i), from; the stream of combined data CZ_(i-1) of the preceding channel, the data stream Z_(i), of the current reception channel, and the weighting coefficient α_(i) of the current channel, and wherein CZ_(i)=α_(i)×CZ_(i-1)+(1−α_(i))×Z_(i).
 5. The apparatus according to claim 1, wherein the calculation module of each reception channel following the first reception channel comprises a synchronization module configured to synchronize the stream of combined data and the combined confidence index issued by the preceding reception channel, and the data stream and the confidence index issued by the current reception channel.
 6. The apparatus according to claim 1, wherein each reception channel comprises means for formatting the received data stream, said means for formatting comprising at least one of the following elements: a tuner, an amplifier and a converter.
 7. The apparatus according to claim 1 wherein the input is a multi-carrier signal.
 8. The apparatus according to claim 7, wherein the input signal is an OFDM or COFDM signal.
 9. The apparatus according to claim 7, wherein the input signal include receive television signals. 